Production of dihydrogen from metallurgical silicon

Abstract

Production of dihydrogen from metallurgical silicon. The present invention relates to a process for the production of dihydrogen, comprising a step of contacting: - hydrogenated silicon obtained by contacting a silicon substrate with an acid, the silicon substrate having a purity of 99.99% or less, - an alkaline solution, thereby generating dihydrogen. Figure for the abstract: None

Description

Title of the invention: Production of dihydrogen from metallurgical silicon

[0001] The present invention relates to the use of hydrogenated silicon, in particular hydrogenated metallurgical silicon, to produce dihydrogen.

[0002] The present invention also relates to a process for the production of dihydrogen from hydrogenated silicon, in particular hydrogenated metallurgical silicon.

[0003] Dihydrogen is a raw material widely used in industry (synthesis of basic molecules such as ammonia, hydrocracking reactions etc...), and is also a source of hydrogen, in particular for fuel cells and hydrogen cars.

[0004] Traditionally, the formation of dihydrogen relies on the catalytic reforming reaction, involving fossil resources. However, the development of renewable energies (wind and photovoltaic energy, for example) has made it possible to consider methods of producing green hydrogen by water electrolysis, and dihydrogen is now one of the most promising renewable energy carriers.

[0005] However, these methods are subject to the presence of a system for capturing this renewable energy (typically solar or wind), and to the power variability inherent in these energy sources. The production of dihydrogen therefore generally involves a preliminary storage step, either direct or indirect.

[0006] Thus, it is known to store dihydrogen directly in cryogenic or pressurized tanks. This storage system requires the use of storage equipment that is not suitable for applications requiring the use of portable (or mobile) devices, such as mobile phones. Furthermore, cryogenic tanks are hampered by the poor efficiency of the dihydrogen liquefaction process. Pressurized tanks, for their part, pose a safety problem.

[0007] As a result, the storage of dihydrogen as an energy carrier is one of the limitations to the development or miniaturization of fuel cells.

[0008] As described in FR 2 915 742, the inventors previously proposed an alternative source of dihydrogen, using hydrogenated silicon in contact with an alkaline solution to produce dihydrogen. Although a technically suitable alternative for the production of dihydrogen, particularly for portable applications, this solution is not very inexpensive. Indeed, the substrate of The silicon used to prepare hydrogenated silicon is primarily a bulk silicon substrate with a high degree of purity, and therefore a high production cost. Furthermore, the preparation of hydrogenated silicon requires an electrochemical treatment, typically an anodizing step, to generate porosity within the substrate. This porosity is advantageous for increasing the hydrogen production rate, and this electrochemical treatment step also has a cost. Moreover, these requirements regarding silicon quality and the treatment step complicate the process and increase its environmental footprint.

[0009] One object of the invention is therefore to propose a source of dihydrogen enabling the efficient production of dihydrogen as needed, without implementing a storage or restitution step of the aforementioned type, and in particular according to a process presenting a reduced financial and / or environmental cost.

[0010] To this end, the invention relates to a process for the production of dihydrogen, comprising a contacting step:

[0011] - of hydrogenated silicon obtained by contacting a silicon substrate with an acid, the silicon substrate having a purity less than or equal to 99.99%,

[0012] - with an alkaline solution,

[0013] that by which dihydrogen is generated.

[0014] The present invention also relates to the use of hydrogenated silicon to provide dihydrogen intended to be recovered and / or valorized, where the hydrogenated silicon is brought into contact with an alkaline solution, said hydrogenated silicon being obtained by bringing into contact with an acid a silicon substrate having a purity less than or equal to 99.99%.

[0015] The entirety of this description applies equally to the process according to the invention and to the use according to the invention.

[0016] Preferably, the silicon substrate has a purity of less than or equal to 99.9%, preferably less than or equal to 99.5%, preferably less than or equal to 99%, preferably between 90% and 99.99%, preferably between 98% and 99%.

[0017] The purity of the silicon substrate indicates the molar content of silicon atoms relative to all the atoms in the substrate, and is therefore related to the amount of impurities. Typically, a silicon substrate containing at most 1019 cm³ of impurities (which is not according to the invention) has a purity of at least 99.999%, this purity being greater than the purity of a silicon substrate (according to the invention) having a purity less than or equal to 99.99%.

[0018] In particular, the silicon substrate may be a metallurgical-grade silicon substrate, or metallurgical silicon. Metallurgical silicon is sometimes denoted MG-silicon, MG meaning "metal grade".

[0019] Preferably, the hydrogenated silicon is in powder form.

[0020] Preferably, the hydrogenated silicon powder has a median particle size D50 between 0.050 pm and 300 pm, preferably between 1 pm and 50 pm, preferably between 1 pm and 15 pm.

[0021] Preferably, the silicon substrate is in powder form.

[0022] Preferably, the silicon powder has a median particle size D50 between 0.050 pm and 300 pm, preferably between 1 pm and 50 pm, preferably between 1 pm and 15 pm.

[0023] The median particle size D50 is determined by wet particle size analysis using laser diffraction (ISO 13320:2020 standard) and image analysis (ISO 13322-1:2014 standard).

[0024] The use of powder allows, among other things, for an increase in the specific surface area of ​​the silicon substrate and, for a given volume, results in a greater quantity of hydrogen atoms present on the surface of the hydrogenated silicon powder, and therefore a higher hydrogen production rate. Conversely, the smaller the particle size of the silicon substrate, the greater the specific surface area, and therefore the greater the quantity of silica to be removed by acid treatment, which reduces the final yield. The quantity of acid required to prepare the hydrogenated silicon powder is also greater. The median particle size of the powders is therefore a compromise between, on the one hand, the hydrogen production rate and, on the other hand, the gross yield for the same quantity of silicon substrate and the quantities of acid to be used and resulting by-products to be treated after the preparation of the hydrogenated silicon.

[0025] According to the invention, a reaction of an alkaline solution on hydrogenated silicon is implemented.

[0026] The alkaline solution reacts on the silicon-hydrogen layer on the surface of the hydrogenated silicon, thus releasing dihydrogen while forming a new silicon-hydrogen layer.

[0027] The production of dihydrogen according to the invention can be schematically summarized by the following reaction (I):

[0028] -Si-Si-H + 4H2O -> -Si-H + Si(OH)4 + 2H2 (I)

[0029] One advantage of using the aforementioned reaction is to allow the production of dihydrogen in a single step, thus generating a lower production cost than that of devices requiring two or more steps, which generally use often expensive intermediate compounds.

[0030] Furthermore, reaction (I) simultaneously induces a reactivation of silicon by reforming silicon-hydrogen bonds on the surface. On this basis, dihydrogen can be produced again on demand by a new implementation of reaction (I).

[0031] Furthermore, thanks to the use of reaction (I), dihydrogen is supplied without having to resort to a storage step prior to release.

[0032] An advantage of the process and use of the invention is that all of the hydrogenated silicon is available to react with the alkaline solution and thus generate dihydrogen, unlike some prior art alternatives in which only the surface of the material is used to store dihydrogen. Therefore, in the process and use of the invention, the amount of dihydrogen available per unit of time depends, in particular, on the amount of silicon present. The amount of dihydrogen is approximately two moles of dihydrogen per mole of hydrogenated silicon, or approximately 1.6 L of dihydrogen per gram of hydrogenated silicon at atmospheric pressure and room temperature.

[0033] The production rate of dihydrogen is rather related to the pH and temperature of the alkaline solution, as well as to the particle size of the hydrogenated silicon.

[0034] The process preferably includes a step of recovery and / or valorization of the dihydrogen formed, for example the use of the dihydrogen as fuel.

[0035] Preferably, the alkaline solution is an aqueous alkaline solution having a pH greater than or equal to 10, preferably between 10 and 14, preferably between 11 and 14.

[0036] Preferably, the alkaline solution is an aqueous solution of NaOH and / or KOH and / or NH40H.

[0037] Preferably, the water in the alkaline solution can be mineral water, salt water, or distilled water.

[0038] In the process and use of the invention, the contact temperature of the alkaline solution and the hydrogenated silicon is generally between approximately 0°C and approximately 80°C, preferably between 15°C and 65°C. According to one embodiment, the contact temperature of the alkaline solution and the hydrogenated silicon is between 10°C and 45°C, preferably between 15°C and 30°C, and preferably between 15°C and 25°C. According to another embodiment, the contact temperature of the alkaline solution and the hydrogenated silicon is between 40°C and 80°C, preferably between 50°C and 65°C.

[0039] The reaction preferably takes place at atmospheric pressure or at slightly higher pressures, generally less than or equal to 3 bars, preferably between 1 bar and 2 bars.

[0040] Preferably, the acid in the step of preparing hydrogenated silicon is hydrofluoric acid.

[0041] After contact with the acid, all or part of the surface of the silicon substrate, in particular the silicon powder, comprises silicon atoms linked to hydrogens, (surface -Si-H groups), suitable for carrying out the aforementioned reaction (I).

[0042] Preferably, the process according to the invention includes a step for preparing hydrogenated silicon comprising contacting the silicon substrate with an acid. Preferably, this step for preparing hydrogenated silicon is free of electrochemical treatment, such as electrochemical anodizing.

[0043] Electrochemical anodizing carried out on a silicon substrate (for example monocrystalline, polycrystalline or amorphous) typically makes it possible to obtain a silicon substrate that is both mesoporous and / or microporous and hydrogenated, which makes it possible to increase the specific surface area of ​​the substrate and therefore its hydrogen storage capacity.

[0044] Preferably, the process according to the invention comprises a step of grinding a silicon substrate with a particle size strictly greater than 300 µm until a powder is obtained with a median particle size D50 between 0.050 µm and 300 µm, preferably between 1 µm and 50 µm, and preferably between 1 µm and 15 µm. This grinding step precedes the step of preparing the hydrogenated silicon. This step can be carried out by any technique known to those skilled in the art.

[0045] Once all of the hydrogenated silicon has reacted, a solution including Si(OH)4 is obtained.

[0046] The Si(OH)4 formed can advantageously be recycled and / or dehydrated or diluted to serve, for example, as a fertilizer.

[0047] The dihydrogen produced by the process according to the invention is intended to be used in any application requiring the use of dihydrogen.

[0048] It can, for example, be used:

[0049] - to power fuel cells and produce electricity, in particular for mobile applications,

[0050] - as fuel, particularly in internal combustion engines, burners (camping stove),

[0051] - as a reagent, for example for decarbonizing internal combustion engines.

[0052] The present invention therefore also relates to the use of the process according to the invention to produce dihydrogen for (or the invention relates to the use of the dihydrogen produced by the process according to the invention to) produce electricity, in particular for (or to) power a fuel cell, the fuel cell preferably being used for a portable application such as a portable electronic device or a vehicle (car, bicycle, for example) or used in a stationary installation, for example for supplying buildings with electricity.

[0053] The process or use of hydrogenated silicon according to the invention is therefore in particular for producing dihydrogen intended for the production of electricity, in particular intended to power a fuel cell, preferably used for a nomadic application such as a portable electronic device or a vehicle (car, bicycle, for example) or used in a stationary installation, for example for supplying buildings with electricity.

[0054] The invention therefore also relates to a method of electricity production, comprising a stage of production of dihydrogen by implementing the dihydrogen production method according to the invention, and a stage of bringing this dihydrogen into contact with dioxygen, for example by means of a fuel cell.

[0055] The present invention also relates to the use of the process according to the invention to produce dihydrogen as (or the invention relates to the use of the dihydrogen produced by the process according to the invention as) a reagent, in particular as a reagent in a chemical synthesis reaction, for example for the production of ammonia, methane or methanol, or in a catalytic cracking reaction or in a hydrogenation reaction, or as a reagent in a process for descaling a heat engine.

[0056] The process or use of hydrogenated silicon according to the invention is therefore particularly for producing dihydrogen as a reagent, in particular as a reagent in a chemical synthesis reaction, for example for the production of ammonia, methane or methanol, in a catalytic cracking reaction or in a hydrogenation reaction, or as a reagent in a thermal engine decarbonizing process.

[0057] The invention therefore also relates to a chemical synthesis process for a product, comprising a step of producing dihydrogen by implementing the dihydrogen production process according to the invention, and a step of contacting the dihydrogen produced with a second reagent intended to react with the dihydrogen to form the product

[0058] The present invention also relates to the use of the process according to the invention to produce dihydrogen as (or the invention relates to the use of the dihydrogen produced by the process according to the invention as) fuel, to produce energy and in particular heat, in particular in internal combustion engines or burners.

[0059] The process or use of hydrogenated silicon according to the invention is therefore particularly for producing dihydrogen as a fuel, especially in internal combustion engines or burners.

[0060] The invention therefore also relates to a process for producing energy, in particular heat, comprising a stage of producing dihydrogen by implementing the process of producing dihydrogen according to the invention, and a stage of burning this dihydrogen.

[0061] According to another aspect, the invention relates to a fuel cell comprising a dihydrogen-operating anode associated with a dihydrogen supply device, this device comprising hydrogenated silicon brought into contact with an alkaline solution to generate dihydrogen by implementing the process according to the invention.

[0062] Hydrogenated silicon in contact with the alkaline solution allows, as illustrated in equation (I), the generation of two equivalents of dihydrogen by regenerating a silicon-hydrogen bond on the surface of the silicon.

[0063] An advantage of the process according to the invention is that it regenerates hydrogenated silicon in situ during fuel cell operation. Consequently, for the same quantity of silicon, the amount of available dihydrogen is greater than that of a device containing only chemisorbed dihydrogen on the surface of the silicon substrate, particularly a porous silicon substrate. The fuel cell operating time therefore depends on the amount of silicon substrate initially introduced.

[0064] Preferably, the hydrogen supply device for feeding the anode of the fuel cell according to the invention comprises a reservoir including a first compartment filled in part or in whole with hydrogenated silicon, preferably this first compartment includes a first zone comprising the hydrogenated silicon and a second zone for contact with the anode and intended to receive the hydrogen formed.

[0065] According to a preferred mode, the reservoir is of the interchangeable type and therefore plays the role of both a hydrogenated silicon loading system and a recovery system for by-products (in particular Si(OH)4) from reaction (I)).

[0066] According to one embodiment, the fuel cell's hydrogen supply device includes a hydrogenated silicon loading system. This system allows for the initial introduction of hydrogenated silicon. Furthermore, additional hydrogenated silicon can be reintroduced into the fuel cell's hydrogen supply device via this loading system when the initially present hydrogenated silicon is completely consumed or when it is consumed beyond a certain threshold, for example, beyond 75%, or even 85%, or better yet, 95% of the initially present hydrogenated silicon. The hydrogenated silicon loading system can be an external loading system or a system allowing the exchange of a cartridge containing the hydrogenated silicon.

[0067] Hydrogenated silicon can be contained in a removable container, for example a cartridge that can be hermetically snapped onto the fuel cell.

[0068] Most often, the cathode of the cell operates with dioxygen. According to this embodiment, the anode and the cathode preferably comprise a medium diffusing dihydrogen and dioxygen, as well as a catalyst and a proton conductor.

[0069] The diffusing medium is also an electronic conductor and is, for example, made of woven carbon fibers in which porous graphite particles are embedded. In this case, gas molecules pass through the mesh of the woven fibers, and electrons are carried by the carbon fibers. According to another embodiment, it is also made of a gas-permeable crosslinked polymer such as PDMS (polydimethylsiloxane) loaded with porous graphite particles.

[0070] The catalyst consists of finely divided platinum incorporated into porous graphite particles.

[0071] According to one embodiment, the catalyst consists of platinum nanoparticles (typically of dimensions between 2 and 50 nm) coated with proton-conducting molecules by chemical grafting and dispersed in a matrix, such as PDMS, permeable to water and gases at a concentration above the percolation threshold in order to allow electronic and proton conductivity.

[0072] The proton conductor is, for example, an ionomer such as Nafion® or consists of molecules bearing groups identical to those used to make the membrane and grafted onto the surface of the catalyst grains. The proton conductor is, in this case, a molecule or macromolecule comprising at least one group capable of capturing and then releasing a proton so that the proton circulates within the generator. The group capable of capturing and then releasing a proton is chosen from among the sulfonate (-SO3) or carboxylate (-COO) groups. In particular, it is advantageous to use a molecule or macromolecule with a fluorinated backbone, which notably increases proton mobility.

[0073] The oxygen is supplied, for example, from a reservoir of air, preferably enriched air, a reservoir containing pure oxygen, or ambient air. The oxygen is transported, for example, by means of a pipe or equivalent from the reservoir to the cathode. The cathode is provided with an opening through which the pipe or equivalent is attached.

[0074] The overall operation of the cell is summarized by the following reaction:

[0075] 2H2+ O2 2H2O (II)

[0076] The battery may include a membrane, for example a porous silicon membrane whose internal surface is chemically grafted with conductors protonics, in particular molecules bearing at least one sulfonate (-SO3) or carboxylate (-COO) group.

[0077] According to another embodiment, the membrane is made of porous silicon whose pores are filled with an ionomer such as Nafion®. The membrane conducts the protons resulting from the operation of the fuel cell but is impermeable to hydrogen and oxygen gas.

[0078] According to an advantageous embodiment, the membrane is an anionic membrane as described in application EP 3050145, or an anionic membrane as described in application EP 4052316, or an ionic conducting membrane as described in application FR 3146240.

[0079] The invention will be further illustrated by reading the examples that follow, given only by way of non-limiting purpose.

[0080] EXAMPLES

[0081] Example 1: Preparation and characterization of hydrogenated silicon powders

[0082] Upon contact with atmospheric oxygen, silicon forms silica SiO2. Any powder Silicon therefore includes a layer of SiO2 on the surface of each particle, which should be eliminated in favor of Si-SiH bonds, for example by treating the metallurgical silicon powder in a hydrofluoric acid bath.

[0083] In this example, four metallurgical silicon powders were treated with hydrofluoric acid according to the following protocol: the powder is weighed in a polypropylene beaker and then covered with an excess of hydrofluoric acid at 40 wt% in deionized water. The silica is removed according to the reactions below: 4- 2¾O (1) = -1619 - 2 * 285 + 910 + 4 * 273 = -187 fy / mol 5¾ + 2HF (2| â / F = —2114 - 2» 285 + 1615 + 2 * 273 = -525 kj / mol

[0084] which gives the following overall: 51¾ 4- 6HF -* / 7.5¾ 4- 2^0 (3) AH" = -2.114 - 2 * 285 + 910 + 6 * 273 = -137 Jÿ / moÉ

[0085] Initially, swelling of the powder and bubbles are observed, corresponding to the formation of SiF4 gas in reaction (1). This reaction is exothermic; the beaker heats up. Then the silica dissolves according to reaction (2). The metallurgical silicon powder grains are then stripped of their oxidation layer and react with hydrofluoric acid to form a layer of Si-Si-H passivation. The hydrogenated powder is then dried on a hot plate to remove excess hydrofluoric acid solution and is stored away from moisture and oxygen.

[0086] The hydrogenated powders are then characterized by determining their median particle size D50 according to the method described in the description. Their bulk density is also determined by calculating the ratio between the mass of a given quantity of powder and the volume that this powder occupies in a graduated container.

[0087] The results obtained are presented in the following table:

[0088] [Tables] Powder A Powder B Powder C Powder D Median particle size (D50) (µm) 5.753 0.157 0.139 14.00 Bulk density (g / cm³) 1.256 0.7261 0.5772 1.041

[0089] Example 2: Generation of dihydrogen from hydrogenated silicon powders

[0090] The hydrogenated silicon powders of Example 1 were used to generate dihydrogen according to the process of the present invention, according to the following reaction: If - SiX + 4^0 If - H + + 2¾ AH =. 2^(¾) + ^($(0#)«) + - 4 * = 0 + (-1342) - 4 * (-285) = -198kJ / mVl

[0091] The process was implemented according to the following protocol:

[0092] 0.30 g of hydrogenated silicon powder is weighed into a vial. This vial is A sealed tube is connected to an inverted graduated tube filled with water. Approximately 100 mL of a potassium hydroxide solution with a pH between 11 and 14 is added, and the tube is then sealed. The KOH solution may or may not be heated, and its pH is more or less basic (between 11 and 14). The solution is stirred, and hydrogen gas gradually fills the graduated tube, allowing the total volume of hydrogen produced to be measured. The hydrogen gas flow rate over time was also measured by filming the graduated tube during the reaction (as it gradually filled with gas) and analyzing the images.

[0093] This protocol was implemented on the four powders of Example 1, at different temperatures. The reaction yield was calculated on the basis of a complete reaction with excess water, according to the following calculation: = = * 2x = * 2^^ = Mp. «2^^ = 2 «2 «

[0094]

[0095]

[0096] VL = = ^SW11_ ayeCo„ =0.089ç / L 2 S fi. 74¾ 0.6 2S ' w2 The results obtained are presented in the following table: [Tables2] Powder A Powder B Powder C Powder D Temperature (°C) 17.0 58 16.5 57.5 16.4 58.5 12.1 57.6 pH 13.8 13.6 13.5 13.7 13.5 13.6 13.6 13.4 Maximum Flow Rate (g / s) 4.4 10⁵ 2.4 10⁴ 1.0 10⁴ 5.8 10⁴ 1.5 10⁴ 7.8 10⁴ 2.7 10⁵ 2.4 10⁴ Total Quantity of Dihydrogen Formed (mL) 490 445 490 405 435 395 450 460 Yield (%) >99 91 >99 83 90 82 92 94 These results illustrate that the smaller the median particle size of the hydrogenated silicon powder, the higher the maximum flow rate. The particle size of the hydrogenated silicon powder therefore influences the kinetics of the dihydrogen production reaction. Temperature also affects the flow rate, which increases by at least a factor of 10 when rising from approximately 16°C to approximately 58°C. However, the total amount of dihydrogen formed depends primarily on the amount of silicon and is therefore similar for each trial (within measurement uncertainties).

Claims

Demands

1. A process for the production of dihydrogen, comprising a step of contacting: - hydrogenated silicon obtained by contacting a silicon substrate with an acid, the silicon substrate having a purity less than or equal to 99.99%, - with an alkaline solution, thereby generating dihydrogen.

2. Use of hydrogenated silicon to provide dihydrogen for recovery and / or valorization, wherein the hydrogenated silicon is brought into contact with an alkaline solution, said hydrogenated silicon being obtained by contacting an acid with a silicon substrate having a purity of less than or equal to 99.99%.

3. A method according to claim 1 or use according to claim 2, wherein the silicon substrate has a purity of less than or equal to 99.9%, preferably less than or equal to 99.5%, preferably between 90% and 99.99%.

4. A method according to claim 1 or 3 or a use according to claim 2 or 3, wherein the hydrogenated silicon is in powder form and / or the silicon substrate is in powder form.

5. A method or use according to claim 4, wherein the silicon powder has a median particle size D50 between 0.050 pm and 300 pm and / or wherein the hydrogenated silicon powder has a median particle size D50 between 0.050 pm and 300 pm.

6. A method according to any one of claims 1 or 3 to 5 or a use according to any one of claims 2 to 5, wherein the alkaline solution is an aqueous alkaline solution having a pH greater than or equal to 10, preferably is an aqueous solution of NaOH and / or KOH and / or NH4OH.

7. A method according to any one of claims 1 or 3 to 6 or a use according to any one of claims 2 to 6, wherein the acid is hydrofluoric acid.

8. A method according to any one of claims 1 or 3 to 7, comprising a step of preparing hydrogenated silicon including contacting the silicon substrate with an acid, said step of preparation of hydrogenated silicon being devoid of electrochemical treatment.

9. Use of the process according to any one of claims 1 or 3 to 8 to produce dihydrogen for the production of electricity, in particular for powering a fuel cell, preferably a fuel cell used for a mobile application or in a stationary installation.

10. Use of the process according to any one of claims 1 or 3 to 8 to produce dihydrogen as a reactant, in particular as a reactant in a chemical synthesis reaction.

11. Use of the process according to any one of claims 1 or 3 to 8 to produce dihydrogen as a fuel, to produce energy and in particular heat.